Method and apparatus for processing semiconductor devices in a singulated form

ABSTRACT

Improved methods and apparatus are provided for the handling and testing of semiconductor devices. One embodiment comprises a die carrier for one or more semiconductor dice having very fine pitch electrical I/O (input/output) elements. The semiconductor dice are temporarily attached to the die carrier in singulated form to enable testing the dice with conventional contact technology. The die carrier may include a flex circuit base substrate and a rigid support frame. Further embodiments comprise materials and methods for attaching the semiconductor dice to the die carrier and for providing a temporary electrical connection with the semiconductor dice during testing. Exemplary materials for providing the temporary electrical connection may comprise a conductive film or tape, a conductive or conductor-filled epoxy, resin or RTV adhesive-based materials, a water-soluble material impregnated with a conductive filler or non-reflowed solder paste.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the handling ofsemiconductor devices during processing. More particularly, the presentinvention relates to a die carrier for one or more semiconductor dicehaving very fine pitch electrical I/O (input/output) elements. Thesemiconductor dice are temporarily attached to the die carrier insingulated form to allow testing the dice with standard contacttechnology. The present invention further relates to materials andmethods for temporarily attaching the dice to the die carrier.

[0003] 2. State of the Art

[0004] In semiconductor manufacturing, it is highly desirable to testsemiconductor devices for functionality prior to packaging or mountingof the devices to higher-level assemblies. By doing so, defectivedevices can be identified and eliminated without unnecessarily providingthem with further processing.

[0005] A common method for testing semiconductor devices duringprocessing comprises forming temporary electrical connections to thedevice I/O elements with pin-type contact probes. Probe testing has beenconventionally carried out, for example, while a plurality ofsemiconductor devices are still contained within a wafer. With thisprocess, a matrix of contact probes carried by a test contactersubstrate is forced against the I/O elements (e.g., bond pads orconductive bumps) of the semiconductor devices in the wafer, and a brieftest is conducted to determine the functionality of each device. Thewafer is subsequently singulated to provide individual semiconductordice. Any dice containing nonfunctional integrated circuits arescrapped, routed for rework if possible, or binned into a category notrequiring full functionality for less demanding applications. Theremaining dice are passed on to further processing for packaging orattaching the dice to higher-level assemblies. By using this method,semiconductor devices may be tested without substantially slowing downthe manufacturing process.

[0006] Probe testing of semiconductor devices at the wafer level,however, is typically capable of providing only a minimal measure offunctionality and does not ensure that the devices will operate suitablyafter final processing in die form. Further, defective devices mayinduce undetectable failures in adjacent devices by testing them whilecoexistent on a wafer, or devices may be damaged during wafersingulation. Accordingly, the dice must be tested again after beingpackaged or otherwise incorporated into higher-level assemblies.Processing unusable semiconductor dice to this point, only to scrap themafter testing, results in a waste of production time and materials.Furthermore, as semiconductor device geometries shrink, the I/O elementsof a die become more difficult to contact and test due to tighteralignment tolerances and the need to use smaller, more fragile contactprobes.

[0007] In order to address the problems associated with testingsemiconductor devices at the wafer level, manufactures have developedmethods for testing of individual, unpackaged semiconductor dice. Themethods often employ temporary die carriers to hold one or moreindividual dice and prevent damage during testing. A prior art diecarrier typically comprises a base portion with a cavity for housing adie and providing an electrical connection to external test circuitry. Adie is placed in the cavity circuit side down, and the die I/O elementsare biased against an array of interconnects in communication withconductive elements on the exterior of the carrier. The interconnectsmay take the form of bumps, pins or simple pads forming a land-gridarray (LGA), depending on whether the die I/O elements are bond pads, orinclude structures such as conductive bumps added for subsequentflip-chip or TAB (tape-automated-bonding) type circuit connection.Biasing the I/O elements against the interconnects is achieved throughthe use of lids, clips or springs that are attached to the base portionand press on the die. Once the die is secured, the carrier is pressedinto a test socket to connect the carrier conductive elements to theexternal test circuitry.

[0008] Prior art die carriers of the type discussed above are disclosedin U.S. Pat. No. 5,367,253 to Wood et al., U.S. Pat. No. 5,517,125 toPosedel et al., U.S. Pat. No. 5,767,689 to Tokuno et al. and U.S. Pat.No. 6,278,286 to Farnworth et al. Although these die carriers overcomesome of the problems associated with testing at the wafer level, theyraise other issues which are undesirable in the context of semiconductorprocessing. Due to their complex structure, existing die carriers may beexpensive to fabricate and include features susceptible to damage duringuse. Interconnects in the form of bumps or pins, for instance, may bedamaged or worn down by repetitive biasing against die I/O elements,especially when the interconnects are of a small size suitable forinterfacing with very fine pitch I/O elements. Likewise, the carrierconductive elements, which may comprise pins or lead-like structures,may be damaged during insertion into a test socket and do not offer theefficiency of probe-type testing. Furthermore, the lids, clips andsprings used to press on a die add cumbersome manual operations to themanufacturing process.

[0009] In view of the present state of the art, there exists a need fora die carrier having a durable, yet simple construction and that uses animproved method for temporarily attaching one or more semiconductor diceto its interconnects.

BRIEF SUMMARY OF THE INVENTION

[0010] The present invention overcomes the deficiencies of the prior artwith a die carrier that is capable of holding and protecting one or moresemiconductor dice without requiring complex or expensive structuralfeatures. The die carrier enables the use of efficientcontact-probe-type testing, without the drawbacks of testing at thewafer level. In its basic form, the die carrier comprises a planar basesubstrate having a pattern of conductive traces with attachment padscorresponding to the I/O elements of a die. The traces fan out from theI/O elements to contact pads that are spaced to interface with aconventional matrix of contact probes. The die carrier of the presentinvention does not require additional structures to hold a die in placeand bias it against the attachment pads. Instead, a die is temporarilyattached to the die carrier by an electrically conductive adhesivematerial placed over the I/O elements on the face of the die. Individualsemiconductor dice may thereby be tested for functionality withoutunduly adding to the cost or complexity of processing.

[0011] In one exemplary embodiment of the die carrier of the presentinvention, the base substrate of the die carrier comprises a flexcircuit. Flex circuits, as known in the art, typically comprise one ormore sheets of polyimide or polyester material having thin, foil-liketraces of metal, alloys, or other conductive materials formed on thesurfaces of the sheets. This construction allows a flex circuit to bendor twist without being damaged, unlike more rigid conventional laminatedcircuit boards. Flex circuits, at least when formed with two circuitlayers or less, are also less expensive to produce than conventionallaminated circuit boards. The low cost associated with fabricating aflex circuit makes it desirable for use as a base substrate for the diecarrier. Furthermore, the pliant nature of a flex circuit allows it toyield when forced against contact probes. This characteristic reducesstress on the test equipment and improves the electrical connection withI/O elements by pressing the flex circuit towards an attached die.

[0012] In a further embodiment of the die carrier of the presentinvention, a support frame is secured to the die-side surface of thebase substrate. The support frame comprises a planar substrate having atleast one aperture for exposing the attachment pad area of the diecarrier and at least partially surrounding the sides of an attached die.By surrounding an adhesively attached die, the support frame helps toprevent the die from being damaged or inadvertently knocked off the diecarrier during handling. When using a flex circuit as a base substrate,the support frame adds rigidity to the die carrier while still allowingthe flex circuit to yield under the attachment pad areas. The supportframe may be secured to the die carrier with an adhesive, by press-fitelements, or by any other suitable means as known in the art.

[0013] Mechanical alignment features may further be included on the diecarrier to aid in aligning the die carrier with a matrix of contactprobes. According to one embodiment of the present invention, thealignment features comprise apertures or notches formed through the basesubstrate, the support frame of the die carrier, or both.

[0014] Additional embodiments of the present invention are directed tothe adhesive materials and methods used for temporarily attaching a dieto the die carrier.

[0015] In one exemplary embodiment of the present invention, theadhesive material comprises an electrically conductive adhesive tapeapplied to the die-side surface of the die carrier over the attachmentpads. A die is placed in a facedown orientation on the tape and isthereby attached to the die carrier. The conductive properties of thetape provide an electrical connection between the I/O elements on thedie and die carrier attachment pads. After the completion of testing,the die may be removed from the die carrier by simply pulling it off thetape. Suitable conductive adhesive tapes are known in the art andtypically function by anisotropic, or z-axis, conduction between thesides of the tape. The tape may further comprise a pressure-sensitiveadhesive tape, which only conducts transverse to the plane of the tapewhen pressure is applied. This may be desirable when the base substrateof the die carrier comprises a flex circuit that is pressed against anattached die during testing.

[0016] In another exemplary embodiment of the present invention, theadhesive material comprises an electrically conductive liquid, gel orpaste that is applied to die carrier attachment pads. The material maycomprise, for example, a conductive or conductor-filled epoxy, resin orroom temperature vulcanized (RTV) silicon or similar material. In someinstances, a die may be bonded to the die carrier by curing the epoxy,resin, or RTV adhesive and then using a solvent or deactivating agent tobreak the bond after the completion of testing. Alternatively, if theepoxy, resin or RTV adhesive material provided sufficient adhesion in anuncured or partially cured (B-stage) state, a die may simply be held inplace without complete curing. After testing, the die is pulled off thedie carrier and cleaned to remove residual epoxy, resin or RTV material.The liquid, gel or paste may also be comprised of a water-solublematerial that sets up with dehydration. The water-soluble material isapplied to the die carrier, and the die placed on the material. Thewater-soluble material is then solidified by ambient or heated drying toform a bond between the die carrier and the die. When testing isfinished, the water-soluble material may simply be washed away withwater and the die removed.

[0017] In yet another exemplary embodiment of the present invention, theadhesive material may comprise a volume of solder paste. As is known inthe art, solder paste comprises fine particles of metals such as tin andlead which are suspended in a flux carrier. Conventional use of solderpaste involves heating it to reflow the particles of metal to a moltenstate and form a permanent bond between conductive elements. As used inthe present invention, solder paste is applied to the die carrierattachment pads, and the die placed on the solder paste. The solderpaste is only heated sufficiently to drive off volatile components ofthe flux without reflowing the metal particles. In this manner, thesolder paste solidifies into a mass of metal particles entrained withindried flux material that bonds the die to the die carrier. As with theabove-described water-soluble material, the solder paste is washed awayafter testing to release the die.

[0018] Other and further features and advantages will be apparent fromthe following detailed description of the present invention when read inconjunction with the accompanying drawings. It should be understood thatthe embodiments described are provided for illustrative and exemplarypurposes only, and that variations to, and combinations of, the severalelements and features thereof are contemplated as being within the scopeof the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0019] In the drawings, which illustrate what is currently considered tobe the best mode for carrying out the invention.

[0020]FIG. 1A shows a sectional side view of a die carrier according tothe present invention.

[0021]FIG. 1B shows the die carrier depicted in FIG. 1A including asupport frame.

[0022]FIG. 2 shows the die carrier depicted in FIG. 1B includingalignment features aligned with a probe tester.

[0023]FIG. 3A shows an exploded perspective view of a die carrier.

[0024]FIG. 3B shows a perspective view of the die carrier depicted inFIG. 3A with the support frame and semiconductor die secured to the basesubstrate.

[0025]FIG. 4A shows a top view of a die carrier for multiple diceincluding a support frame with a single aperture of a size sufficient toat least partially surround all of the multiple dice.

[0026]FIG. 4B shows a top view of a die carrier for multiple diceincluding a support frame having multiple apertures for at leastpartially surrounding each die of the multiple dice.

[0027]FIG. 5 shows a die carrier with a conductive film or adhesive tapefor attaching a semiconductor die.

[0028]FIG. 6 shows a water-soluble mask as conventionally used to holdthrough-hole electronic components.

[0029]FIG. 7 shows a schematic view of a water-soluble bond used toprovide a temporary electrical connection according to the presentinvention.

[0030]FIG. 8A shows a schematic view of a solder paste bond used toprovide a temporary electrical connection with a pad-like structure.

[0031]FIG. 8B shows a schematic view of a solder paste bond used toprovide a temporary electrical connection with a conductive bump.

[0032]FIG. 9 shows a semiconductor die bonded to a die carrier with awater-soluble material deposited around a peripheral edge of thesemiconductor die.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Turning initially to the accompanying drawings, die carrierstructures and materials and methods for temporarily attaching one ormore semiconductor dice thereto are depicted to show various embodimentsof the present invention. Common elements of the embodiments aredesignated with like reference numerals. It should be understood thatthe drawings are not illustrative of actual views of any particularportion of the actual device structures, but are merely idealizedschematic representations which are employed to more clearly and fullydepict the invention.

[0034]FIG. 1A shows a side view of a die carrier 2 structured for useaccording to the present invention. In this embodiment, die carrier 2 isshown in a basic form comprised of a substantially planar base substrate4 configured to hold a single semiconductor die 6. Base substrate 4includes a die-side surface 8 having a pattern of conductive traces 10formed thereon. The first ends of traces 10 comprise attachment pads 12that are positioned on die-side surface 8 in locations corresponding tothe pattern of I/O elements 14, such as bond pads or redistributedexternal contact locations on die 6. The pattern of I/O elements 14 maytake the form of one or more spaced rows on the face of die 6. If I/Oelements 14 are laid out in a fine pitch pattern used with presentcircuit densities, for example, they would comprise rows of elementsspaced or pitched at intervals of about 0.5 mm or less. Of course, anyother arrangement of I/O elements on the face of a semiconductor die maybe accommodated by a die carrier according to the present invention.

[0035] I/O elements 14 are temporarily secured to attachment pads 12 byan electrically conductive adhesive material 16. The specific featuresand embodiments of adhesive materials disclosed by the present inventionare described in further detail below. As shown in FIG. 1A, I/O elements14 are depicted as being pad-like LGA structures such as bare die bondpads. It is to be understood, however, that I/O elements 14 may alsoinclude structures such as conductive bumps added for subsequentflip-chip or TAB-type circuit connection, and that these structures maybe similarly secured by adhesive material 16.

[0036]FIG. 1A further shows that traces 10 fan out from I/O elements 14to a pattern of contact pads 18 that are sufficiently spaced tointerface with a standard matrix of contact probes 34 (FIG. 2). Astandard test matrix, for instance, may conventionally have probesspaced at a pitch of about 0.8 mm or greater. In one arrangement,contact pads 18 are formed on a back surface 20 of base substrate 4 andare electrically connected to the second ends of traces 10 by way ofconductive vias 22. In this manner, die carrier 2 is configured to becontacted from below, as is often the approach used with conventionaltest equipment. In another arrangement, contact pads 18′ are formed ondie-side surface 8 of base substrate 4, thereby allowing die carrier 2to be contacted from above. It is further contemplated that in somecases, passive devices 11 (FIG. 3A) may be included on base substrate 4and connected to traces 10 at points between I/O elements 14 and contactpads 18. When testing high-frequency semiconductor devices, forinstance, the added circuit length from traces 10 may generate signalnoise that is detrimental to the test results. By including passivedevices 11 (e.g. capacitors, resistors or inductors), the signal noisemay be reduced or eliminated.

[0037] In one presently preferred embodiment of die carrier 2, basesubstrate 4 comprises a flex circuit formed of a core of one or moresheets of pliant material. As used herein, the term “pliant material”refers to materials that enable base substrate 4 to be bent, twisted orotherwise reshaped from its substantially planar configuration, such aspolyimide or polyester materials conventionally known for use infabricating flex circuits. Traces 10, attachment pads 12 and contactpads 18 may comprise patterned metal or metal alloy foils formed on thesurfaces of or within the sheets of pliant material, or may comprise oneor more layers of applied conductive polymer materials known for use asconductors in flex circuits. The flex circuit design allows die carrier2 to be easily fabricated without requiring specialized manufacturingprocesses associated with the more complex structures of prior art diecarriers. Furthermore, it is well known that the product life of aspecific semiconductor die layout is relatively short due to constantimprovements in technology. In the past, changing the I/O layout of adie required an expensive retooling to provide new die carriers. The lowcost of a flex circuit reduces the concerns of having to replace diecarriers to accommodate a new die I/O layout.

[0038] In some instances, however, process conditions may require basesubstrate 4 to have a more substantial construction than that offered bya flex circuit. It is, therefore, contemplated that base substrate 4 maybe formed as a rigid structure such as a laminated circuit board of, forexample, FR-4, FR-5, or BT material.

[0039] According to a further embodiment of the present invention, diecarrier 2 includes a support frame 24 as shown in FIG. 1B. Support frame24 comprises a planar substrate having an aperture 26 that exposes thedie attachment area of base substrate 4 and at least partially surroundsthe sides of die 6. Support frame 24 is depicted in FIG. 1B as having athickness that is approximately equal to a thickness of die 6 in orderto completely surround its sides within aperture 26. Support frame 24thereby protects die 6 from being damaged or knocked off of basesubstrate 4 while being handled. Of course, it is within the scope ofthe present invention that support frame 24 may have a lesser or greaterthickness than that of die 6, if so desired. Support frame 24 may beformed of any material known for use with die carriers or othersemiconductor-type fixtures. In the case where base substrate 4 is aflex circuit, support frame 24 should be of a material sufficientlyrigid to maintain the planarity of base substrate 4 during handling andtesting. When base substrate 4 is constructed of a rigid material, themain function of support frame 24 is to protect the sides of die 6, butit may also offer additional rigidity. Plastics, metals, ceramics,laminated glass composites or other common materials would be suitablefor this purpose. Support frame 24 may be temporarily or permanentlysecured to base substrate 4 by any known means. In FIG. 1B, supportframe 24 is depicted as being secured in place by an adhesive layer 28,which may, for example, comprise a dispensed liquid or gel adhesive or atape or film segment coated on both sides with a suitable adhesive.

[0040] Die carrier 2 may also include alignment features 30 that aid itsalignment during testing. FIG. 2 shows the function of alignmentfeatures 30 when die carrier 2 is seated on a probe tester 32. Probetester 32 is schematically shown to include a matrix of contact probes34 carried by a test contacter substrate 36. Contact probes 34 areresiliently biased against contact pads 18 of die carrier 2 to formtemporary electrical connections for the testing of die 6. Probe tester32 further includes alignment pins 38 that extend outwardly from testcontacter substrate 36 to a point above contact probes 34. As shown inFIG. 2, alignment features 30, which in this embodiment are aperturespassing through base substrate 4 and support frame 24, are seated aroundalignment pins 38. In this manner, contact pads 18 of die carrier 2 areforced into alignment with contact probes 34. This ensures a goodelectrical connection will exist for testing die 6. While alignmentfeatures 30 are depicted as comprising apertures passing through basesubstrate 4 and support frame 24, it is to be understood that otherconfigurations are possible and contemplated as being within the scopeof the present invention. For instance, alignment features 30 mightcomprise notches located on the peripheral edge of die carrier 2 thatengage alignment pins 38, or may comprise elements that protrude fromdie carrier 2 and mate with holes formed in test contacter substrate 36.

[0041]FIG. 3A shows an exploded perspective view of die carrier 2 havingbase substrate 4 and support frame 24 for surrounding die 6. As depictedin FIG. 3A, base substrate 4 is configured with traces 10 fanning outfrom four rows of attachment pads 12 to four rows of conductive vias 22overlying contact pads 18 (not shown). A passive device 11 is also shownon base substrate 4 as being connected to a trace 10 for reducing oreliminating signal noise. In this embodiment of die carrier 2, alignmentfeatures 30 comprise notches formed on the peripheral edges of basesubstrate 4 and support frame 24. FIG. 3B shows support frame 24 securedto base substrate 4 and die 6 attached to die carrier 2 within aperture26.

[0042]FIGS. 3A and 3B highlight the utility of using die carrier 2 fortesting of semiconductor dice having very fine pitch I/O elements. Byspreading out the location of contact pads 18, smaller and more fragilecontact probes are not required to match up with the layout of I/Oelements 14 on die 6. Instead, conventional test equipment withconventionally sized and pitched contact probes may be utilized. FIGS.3A and 3B also highlight the benefit of using a flex circuit for basesubstrate 4. Because support frame 24 does not overlie the location ofcontact pads 18, a flex circuit base substrate 4 may yield slightly whenpressed on by contact probes 34. This reduces the stress on the testequipment. Furthermore, in embodiments of die carrier 2 where at leastsome of contact pads 18 are located under die 6, base substrate 4 willbe pushed towards I/O elements 14, thereby improving the electricalconnection through adhesive material 16.

[0043] While FIGS. 1A-3B have depicted die carrier 2 as holding a singlesemiconductor die 6, it is also contemplated that die carrier 2 may beformed to accommodate multiple dice for simultaneous testing. Basesubstrate 4 would simply be formed with attachment pads, traces andcontact pads corresponding to the I/O elements of multiple dice. Supportframe 24 may be provided with an aperture 26′ of sufficient size to atleast partially surround all the dice 6, as shown in FIG. 4A, or may beprovided with multiple apertures 26″, each aperture sized to at leastpartially surround one or more of the dice 6, as shown in FIG. 4B.Alternatively, multiple die carriers, each for holding a singlesemiconductor die, may be placed into a matrix-type fixture and loweredonto an array of sockets on a test board. Each of the die carriers couldbe directly contacted by the test equipment through the fixture, or thefixture itself could include conductive elements providing electricalcommunication between the test equipment and the die carriers.

[0044] Further advantages over the prior art result from the novelmaterials and methods disclosed by the present invention for temporarilyattaching semiconductor dice to a die carrier. FIGS. 5-9 show thespecific features and embodiments of adhesive materials as used inconjunction with the above-described die carrier 2. However, it is alsobelieved that some of the disclosed adhesive materials have notheretofore been used for forming a temporary electrical connectionbetween a semiconductor die and any higher-level assembly and are,therefore, in and of themselves inventive.

[0045] In one embodiment of the present invention, the adhesive materialcomprises an electrically conductive film or adhesive tape 40. FIG. 5shows adhesive tape 40 applied to the die-side surface 8 of die carrier2 over attachment pads 12. Adhesive tape 40 electrically connectsattachment pads 12 on one side thereof to I/O elements 14 of die 6 onthe other side thereof by anisotropic, or z-axis, conduction. As shownin FIG. 5, because adhesive tape 40 only conducts in a directionperpendicular to its two sides (illustrated by arrows in adhesive tape40), a single piece of tape may be applied between attachment pads 12and I/O elements 14 without any shorting occurring between adjacentlocations. After testing, die 6 would be removed from die carrier 2 in amanner similar to that known for removing die from a dicing frame afterwafer singulation. In this process, heat is applied to adhesive tape 40to loosen the bond with die 6, and a vacuum chuck lifts die 6 off ofadhesive tape 40. When base substrate 4 comprises a flex circuit, forcemay also be applied to die carrier 2 underneath die 6 to assist inbreaking the bond.

[0046] Adhesive tape 40 may further comprise a pressure-sensitive z-axisconductive adhesive tape that only conducts when pressure is applied.This may be beneficial, especially when base substrate 4 comprises aflex circuit, in that adhesive tape 40 will not provide an electricalconnection until it is pressed on during testing. Die 6 will, therefore,be electrically isolated when handling die carrier 2 outside of testing,and the risk of damage to die 6 from static charges known to build up inthe processing environment will be avoided. Conductive films andadhesive tapes of the type described are known in the art andcommercially available from vendors such as 3M Corporation of St. Paul,Minn. under the product name Z-Axis Adhesive Film 5303R-1, as well asSheldahl, Inc. of Northfield, Minn., under the product name Z-Link.

[0047] In another embodiment, the adhesive material comprises anelectrically conductive liquid, gel or paste. The liquid, gel or pasteis applied to each of the attachment pads 12 of die carrier 2, asgenerally shown by adhesive material 16 in FIGS. 1A and 1B. One materialsuitable for this embodiment is a conductive or conductor-filled resinor epoxy. Conductive resins and epoxies have conventionally been used insemiconductor manufacturing to permanently bond die I/O elements tohigher-level assemblies. This is accomplished by curing the resins andepoxies after die attachment to form a solidified conductive bondbetween the die I/O elements and conductive elements of the higher-levelassemblies. When used in conjunction with the present invention, theresin or epoxy may be similarly cured to form a solidified conductivebond between attachment pads 12 and I/O elements 14. After testing, thebond would be broken by a solvent or deactivating agent to allow removalof die 6 from die carrier 2. The specific solvent or deactivating agentwould be based on the composition of the resin or epoxy used to bond I/Oelements 14 to attachment pads 12. A suitable solvent might comprise,for example, an alcohol-based fluid capable of breaking down the epoxyor resin in a solvent bath. When using a thermoplastic resin or epoxy,on the other hand, a deactivating agent might comprise heat applied tothe resin or epoxy after testing.

[0048] Another suitable material for this embodiment is a roomtemperature vulcanized (RTV) adhesive of silicon or similar materials,an example of which is commercially available from Henkel Loctite Corp.of Rocky Hill, Conn., under the product name 5421 ElectricallyConductive Adhesive. The RTV adhesive may be impregnated with conductiveparticles such as powdered silver, which would then provide a conductivebond between attachment pads 12 and I/O elements 14. RTV adhesive adherewell to tin/lead coatings that may be commonly used to cover circuitelements such as attachment pads 12, while these adhesives are lessadherent to gold, which is often used for die structures such as I/Oelements 14. Using an adhesive with this characteristic may simplifyremoval of die 6 after testing, bond separation of the cured I/Oadhesive would be more likely to occur at the interface with I/Oelements 14.

[0049] In an alternative to the above embodiments, if the resin, epoxyor RTV adhesive provides sufficient adhesion in an uncured or partiallycured (B-stage) state, die 6 may be held in place during testing withoutcompletely curing the resin, epoxy or RTV adhesive into a solidifiedbond. After testing, die 6 could then simply be pulled off of diecarrier 2 without requiring further processing to break a solidifiedbond between I/O elements 14 and attachment pads 12. Cleaning ofresidual resin, epoxy or RTV adhesive from I/O elements 14 might berequired after separation of die 6 from die carrier 2, but this processwould be much less labor intensive than having to use a solvent ordeactivating agent to break a solidified bond.

[0050] It is also envisioned that the adhesive material in liquid, gelor paste form may comprise a water-soluble material that sets up withdehydration. In the prior art, similar water-soluble mask materials havebeen used to hold through-hole electronic components onto circuit boardsduring wave soldering operations. FIG. 6 shows how a mask material 42 isconventionally applied in the form of a liquid, gel or paste to thesurface of a circuit board 44 along the sides of a through-holecomponent 46. Mask material 42 is then solidified by ambient or heateddrying such that component 46 is bonded to circuit board 44. The entireassembly is passed through a wave solder machine, thereby forming solderjoints 48 between the leads 50 of component 46 and through-holes 52 incircuit board 44. Mask material 42 is thereafter removed by washing itaway with water. Water-soluble mask materials used for this purpose arecommercially available from several vendors, and are typicallyformulated from polymer and/or copolymer materials mixed with an organicsolvent such as an alcohol. Contronic Devices, Inc. of Huntington Beach,Calif., for instance, offers liquid- or paste-type masks under theproduct names “WSM-90T Comp Hold” and “NI Comp Hold 60 LH.” Kester Corp.of Des Plaines, Ill., also offers a similar water-soluble mask under theproduct name TC-564-1.

[0051] These water-soluble masks are not formulated to be conductive innature, and it is believed that they have not previously beencontemplated for use in providing temporary electrical connections.According to the present invention, a water-soluble material, such asthe above-described component masks, is made conductive by impregnatingit with a filler of conductive material particles. This is similar tomethods used for making conductive epoxies, wherein very fine particlesof silver or other conductive materials are added to provide conductivepathways through the epoxy structure.

[0052]FIG. 7 shows the structure of a water-soluble material 54 used inthe present invention to provide a temporary electrical connectionbetween attachment pads 12 of die carrier 2 and I/O elements 14 of die6. In this attachment method, water-soluble material 54 is impregnatedwith conductive particles 56 and applied to each of attachment pads 12.Conductive particles 56 may comprise a powdered metal, such as silver orlead or any other conductive material that may be entrained withinwater-soluble material 54. I/O elements 14 of die 6 are placed intocontact with water-soluble material 54, which is subsequently dehydratedto form a solid bond securing die 6 to die carrier 2. Depending on thecomposition of water-soluble material 54, it may simply be dried overtime in the ambient environment or dried under elevated temperatures.Adjacent, mutually contacting conductive particles 56 form conductivepathways through water-soluble material 54, thereby providing atemporary electrical connection between attachment pads 12 and I/Oelements 14. When testing has been completed, water-soluble material 54is dissolved with water to release die 6 from die carrier 2.

[0053] In another embodiment of the present invention, solder paste isused to attach die 6 to die carrier 2. FIG. 8A shows the structure of avolume of solder paste 58 acting as the adhesive material for bondingI/O elements 14 to attachment pads 12. As known in the art, solder paste58 comprises fine metal particles or spheres 60, such as tin and lead,suspended in a flux carrier 62. Solder pastes of this type arecommercially available from vendors such as Kester Company of DesPlaines, Ill. Flux carrier 62 initially comprises a semifluid media,typically rosin-based with a volatile organic solvent. In the presentattachment method, solder paste 58 is applied to each of attachment pads12, and I/O elements 14 of die 6 are placed on top of solder paste 58.Solder paste 58 is only heated to a point where the volatile solventcomponent of flux carrier 62 evaporates without any melting of metalspheres 60. In this manner, flux carrier 62 sets up into a solidifiedstructure that entrains metal spheres 60 and is adhered to attachmentpads 12 and I/O elements 14. Adjacent, mutually contacting metal spheres60 form conductive pathways through solder paste 58, thereby providing atemporary electrical connection between attachment pads 12 and I/Oelements 14. As with the above-described water-soluble material 54, oncetesting is complete, solder paste 58 is washed away to release die 6from die carrier 2. The wash medium may be water or some other solvent,such as alcohol, suitable for dissolving the composition of flux carrier62.

[0054]FIG. 8B shows an embodiment using solder paste 58 as an adhesivematerial wherein I/O elements 14 are not pad-like structures, but rathercomprise conductive bumps 64 that are used for flip chip or TABconnection. Under this embodiment, conductive bumps 64 are pressed downinto solder paste 58 such that metal spheres 60 and flux carrier 62 areforced up around the sides of conductive bumps 64. The heating of fluxcarrier 62 into a solidified structure is then carried out in the samemanner as described with pad-like I/O elements.

[0055] Although the present invention has been described with respect tothe illustrated embodiments, various additions, deletions andmodifications are contemplated as being within its scope. For instance,die carrier 2 may have a perimeter shape other than rectangular, or maybe dimensioned to fit into standardized handling trays used fortransportation of dice between equipment locations. Likewise, whilesupport frame 24 has been depicted in FIGS. 1A-3B as having a specificsize in relation to base substrate 4, any other dimensions are possible.Support frame 24 may extend beyond the edges of base substrate 4 ormight be comprised of separate elements attached to isolated portions ofbase substrate 4.

[0056] Furthermore, as stated above, the adhesive materials and methodsdisclosed by the present invention may be used for providing a temporaryelectrical connection between electronic devices other than whenattaching a semiconductor die to a die carrier. It is also contemplatedthat an adhesive material may be used for temporarily attaching asemiconductor die to the die carrier without providing an electricalconnection. For example, an adhesive tape may simply be placed over thesupport frame aperture to hold or assist in holding a die in placeduring testing. As shown by dashed lines in FIG. 1B, a section ofadhesive tape 70 is placed across aperture 26 in support frame 24 andholds die 6 in contact with attachment pads 12.

[0057] Likewise, the above-described water-soluble mask material 42 maybe used without any conductive filler and placed around the periphery ofdie 6 to hold I/O elements 14 against attachment pads 12 on basesubstrate 4 during testing, as shown in FIG. 9. Similar to theabove-described wave soldering operations, mask material 42 issolidified by ambient or heated drying such that die 6 is bonded to basesubstrate 4. Die 6 is tested, and mask material 42 is thereafter removedby washing it away with water.

[0058] The scope of the present invention is, therefore, indicated bythe appended claims, rather than the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A die carrier assembly, comprising: a firstsubstantially planar substrate including a die-side surface with atleast one die attachment area for holding at least one semiconductor dieand an opposing back surface; at least one attachment pad located on thedie-side surface of the first substantially planar substrate; at leastone contact pad located on one of the die-side surface and the backsurface of the first substantially planar substrate; at least oneconductive trace connecting the at least one attachment pad and the atleast one contact pad; and a second substantially planar substratesecured to the die-side surface of the first substantially planarsubstrate and including at least one aperture therethrough that exposesthe at least one die attachment area of the die-side surface.
 2. The diecarrier assembly of claim 1, wherein the first substantially planarsubstrate comprises a flex circuit including a core of one or moresheets of pliant material.
 3. The die carrier assembly of claim 2,wherein at least one of the at least one attachment pad, the at leastone contact pad and the at least one conductive trace comprises at leastone layer of a metal, a metal alloy or a conductive polymer material. 4.The die carrier assembly of claim 2, wherein the one or more sheets ofpliant material are comprised of a polyimide or polyester.
 5. The diecarrier assembly of claim 2, wherein the second substantially planarsubstrate comprises a substantially rigid material.
 6. The die carrierassembly of claim 1, wherein the at least one contact pad is located onthe die-side surface of the first substantially planar substrate.
 7. Thedie carrier assembly of claim 1, wherein the at least one contact pad islocated on the back surface of the first substantially planar substrate,and further comprising: at least one conductive via passing at leastpartially through the first substantially planar substrate andconnecting the at least one contact pad to the at least one conductivetrace.
 8. The die carrier assembly of claim 1, further comprising atleast one passive device located on the first substantially planarsubstrate and connected to the at least one conductive trace.
 9. The diecarrier assembly of claim 1, wherein the at least one die attachmentarea comprises a plurality of die attachment areas for holding aplurality of semiconductor dice on the die-side surface of the firstsubstantially planar substrate.
 10. The die carrier assembly of claim 9,wherein the at least one aperture of the second substantially planarsubstrate comprises a single aperture of a size sufficient to expose theplurality of die attachment areas.
 11. The die carrier assembly of claim9, wherein the at least one aperture of the second substantially planarsubstrate comprises a plurality of apertures, each aperture of theplurality of apertures exposing a single die attachment area of theplurality of die attachment areas.
 12. The die carrier assembly of claim1, further comprising at least one alignment feature configured forengaging another alignment feature carried by a probe assembly.
 13. Thedie carrier assembly of claim 12, wherein the at least one alignmentfeature comprises one of an aperture passing at least partially througha portion of the die carrier assembly, a notch on a peripheral portionof the die carrier assembly and a structure protruding outwardly from asurface of the die carrier assembly.
 14. The die carrier assembly ofclaim 1, wherein the at least one attachment pad comprises a pluralityof attachment pads, each attachment pad of the plurality of attachmentpads spaced from an adjacent attachment pad at an interval of about 0.5mm or less.
 15. The die carrier assembly of claim 14, wherein the atleast one contact pad comprises a plurality of contact pads, eachcontact pad of the plurality of contact pads spaced from an adjacentcontact pad at an interval of about 0.8 mm or greater.
 16. The diecarrier assembly of claim 1, further comprising a semiconductor diehaving at least one I/O element, wherein the at least one I/O element isattached to the at least one attachment pad on the first substantiallyplanar substrate with a conductive adhesive material.
 17. The diecarrier assembly of claim 16, wherein the second substantially planarsubstrate has a thickness in a direction perpendicular to the die-sidesurface of the first substantially planar substrate that isapproximately equal to a thickness of the semiconductor die.
 18. The diecarrier assembly of claim 16, wherein the conductive adhesive materialcomprises a z-axis conductive adhesive tape.
 19. The die carrierassembly of claim 18, wherein the adhesive tape is a pressure-sensitivez-axis conductive adhesive tape.
 20. The die carrier assembly of claim16, wherein the conductive adhesive material comprises a resin, epoxy orRTV adhesive-based material.
 21. The die carrier assembly of claim 20,wherein the resin, epoxy or RTV adhesive-based material comprises aconductive or conductor-filled liquid, gel or paste.
 22. The die carrierassembly of claim 20, wherein the resin, epoxy or RTV adhesive-basedmaterial comprises a solidified structure.
 23. The die carrier assemblyof claim 16, wherein the conductive adhesive material comprises an atleast partially solidified water-soluble material impregnated with aconductive filler of discrete particles.
 24. The die carrier assembly ofclaim 23, wherein the conductive filler comprises discrete particles ofa metal or metal alloy.
 25. The die carrier assembly of claim 23,wherein the water-soluble material comprises a polymer orcopolymer-based material.
 26. The die carrier assembly of claim 16,wherein the conductive adhesive material comprises discrete particles ofa metal or metal alloy entrained within a solidified flux carrier. 27.The die carrier assembly of claim 16, wherein the at least one I/Oelement of the semiconductor die comprises a bond pad.
 28. The diecarrier assembly of claim 16, wherein the at least one I/O element ofthe semiconductor die comprises a discrete conductive element extendingoutwardly from the semiconductor die.
 29. The die carrier assembly ofclaim 1, further comprising a semiconductor die having at least one I/Oelement, wherein the at least one I/O element is held against the atleast one attachment pad on the first substantially planar substratewith an adhesive tape extending across the at least one aperture of thesecond substantially planar substrate.
 30. A method for testing anelectronic device comprising: providing a first substantially planarsubstrate including a first conductive element and a second conductiveelement in electrical communication with the first conductive element;attaching a semiconductor die to the first substantially planarsubstrate by adhesively bonding an I/O element of the semiconductor dieto the first conductive element with a conductive material; securing asecond substantially planar substrate to the first substantially planarsubstrate to at least partially surround the semiconductor die; probingthe second conductive element to test a functional aspect of thesemiconductor die; and removing the semiconductor die from the firstsubstantially planar substrate.
 31. The method of claim 30, whereinproviding a first substantially planar substrate comprises forming thefirst substantially planar substrate of one or more sheets of pliantmaterial.
 32. The method of claim 31, further comprising forming atleast one of the first conductive element and the second conductiveelement with at least one layer of a metal, a metal alloy or aconductive polymer material.
 33. The method of claim 31, wherein formingthe first substantially planar substrate of one or more sheets of pliantmaterial comprises forming the one or more sheets of pliant materialfrom a polyimide or polyester material.
 34. The method of claim 31,further comprising forming the second substantially planar substrate ofa substantially rigid material.
 35. The method of claim 30, whereinprobing the second conductive element comprises probing the secondconductive element on a side of the first substantially planar substrateto which the semiconductor die is attached.
 36. The method of claim 30,wherein probing the second conductive element comprises probing thesecond conductive element opposite a side of the first substantiallyplanar substrate to which the semiconductor die is attached.
 37. Themethod of claim 30, further comprising filtering signal noise with atleast one passive device on the first substantially planar substrate.38. The method of claim 30, further comprising attaching a plurality ofsemiconductor dice to the first substantially planar substrate byadhesively bonding at least one I/O element of each semiconductor die ofthe plurality of semiconductor dice to a conductive element on the firstsubstantially planar substrate.
 39. The method of claim 38, furthercomprising at least partially surrounding the plurality of semiconductordice with a single aperture formed in the second substantially planarsubstrate.
 40. The method of claim 38, further comprising at leastpartially surrounding each semiconductor die of the plurality ofsemiconductor dice with a separate aperture formed in the secondsubstantially planar substrate.
 41. The method of claim 30, whereinprobing the second conductive element comprises contacting the secondconductive element with a contact probe, and further comprising:aligning the contact probe with the second conductive element by usingan alignment feature formed on at least one of the first substantiallyplanar substrate and the second substantially planar substrate.
 42. Themethod of claim 30, further comprising: forming a plurality of firstconductive elements spaced at intervals of about 0.5 mm or less on thefirst substantially planar substrate; and attaching the semiconductordie to the first substantially planar substrate by adhesively bonding aplurality of I/O elements of the semiconductor die to the plurality offirst conductive elements with a conductive material.
 43. The method ofclaim 42, further comprising: forming a plurality of second conductiveelements spaced at intervals of about 0.8 mm or greater on the firstsubstantially planar substrate; and probing the plurality of secondconductive elements with an array of contact probes.
 44. The method ofclaim 30, further comprising surrounding the semiconductor die to aheight approximately equal to a thickness of the semiconductor die withthe second substantially planar substrate.
 45. The method of claim 30,wherein adhesively bonding an I/O element of the semiconductor die tothe first conductive element comprises bonding the I/O element to thefirst conductive element with a z-axis conductive adhesive tape.
 46. Themethod of claim 45, further comprising applying a force transverse to amajor plane of the z-axis conductive adhesive tape to convert the z-axisconductive adhesive tape from a nonconductive state to a conductivestate.
 47. The method of claim 30, further comprising applying theconductive material to at least one of the first conductive element andthe I/O element of the semiconductor die in the form of a conductive orconductor-filled liquid, gel or paste.
 48. The method of claim 47,wherein applying the conductive material in the form of a conductive orconductor-filled liquid, gel or paste comprises applying a resin, epoxyor RTV adhesive-based material.
 49. The method of claim 47, furthercomprising probing the second conductive element while the semiconductordie is held in place by the conductive or conductor-filled liquid, gelor paste.
 50. The method of claim 47, further comprising: at leastpartially curing the conductive or conductor-filled liquid, gel or pasteto provide an at least partially solidified bond between the firstconductive element and the I/O element of the semiconductor die; probingthe second conductive element while the semiconductor die is held inplace by the at least partially solidified bond; and breaking the atleast partially solidified bond with a solvent or deactivating agent toremove the semiconductor die from the first substantially planarsubstrate.
 51. The method of claim 47, wherein applying the conductivematerial in the form of a conductive or conductor-filled liquid, gel orpaste comprises applying a water-soluble material impregnated with aconductive filler, and further comprising: dehydrating the water-solublematerial to a degree sufficient to provide an at least partiallysolidified bond between the first conductive element and the I/O elementof the semiconductor die; probing the second conductive element whilethe semiconductor die is held in place by the at least partiallysolidified bond; and breaking the at least partially solidified bond bydissolving it with water to remove the semiconductor die from the firstsubstantially planar substrate.
 52. The method of claim 51, furthercomprising forming the conductive filler of the water-soluble materialfrom discrete particles of a metal or metal alloy.
 53. The method ofclaim of claim 51, further comprising selecting the water-solublematerial to comprise a polymer or copolymer-based material.
 54. Themethod of claim 47, wherein applying the conductive material in the formof a conductive or conductor-filled liquid, gel or paste comprisesapplying a solder paste having discrete particles of a metal or metalalloy entrained within a flux carrier, and further comprising: heatingthe solder paste to provide an at least partially solidified solderpaste structure comprising the discrete particles of a metal or metalalloy entrained within the flux carrier, wherein the at least partiallysolidified solder paste structure forms a bond between the firstconductive element and the I/O element of the semiconductor die; probingthe second conductive element while the semiconductor die is held inplace by the at least partially solidified solder paste structure; anddissolving the at least partially solidified solder paste structure toremove the semiconductor die from the first substantially planarsubstrate.
 55. The method according to claim 54, wherein heating thesolder paste comprises driving off volatiles in the flux carrier whilemaintaining the particles of a metal or metal alloy in a solid statewithin a matrix of remaining material of the flux carrier.
 56. Themethod according to claim 30, wherein adhesively bonding an I/O elementof the semiconductor die to the first conductive element comprisesadhesively bonding a bond pad of the semiconductor die to the firstconductive element.
 57. The method according to claim 30, whereinadhesively bonding an I/O element of the semiconductor die to the firstconductive element comprises adhesively bonding a discrete conductiveelement extending outwardly from the semiconductor die to the firstconductive element.
 58. A circuit assembly comprising: an electronicdevice including a first conductive element; a substrate including asecond conductive element; and an electrically conductive bond joiningthe first conductive element and the second conductive element, whereinthe electrically conductive bond comprises an at least partiallysolidified water-soluble material impregnated with a conductive fillerof discrete particles.
 59. The circuit assembly of claim 58, wherein theconductive filler comprises discrete particles of a metal or metalalloy.
 60. The circuit assembly of claim 58, wherein the water-solublematerial comprises a polymer or copolymer-based material.
 61. Thecircuit assembly of claim 58, wherein the electronic device comprises asemiconductor die.
 62. The circuit assembly of claim 61, wherein thesubstrate comprises a die carrier configured to interface thesemiconductor die with a matrix of contact probes.
 63. A circuitassembly comprising: an electronic device including a first conductiveelement; a substrate including a second conductive element; and anelectrically conductive bond joining the first conductive element andthe second conductive element, wherein the electrically conductive bondcomprises discrete particles of a metal or metal alloy entrained withina solidified flux carrier.
 64. The circuit assembly of claim 63, whereinthe electronic device comprises a semiconductor die.
 65. The circuitassembly of claim 64, wherein the substrate comprises a die carrierconfigured to interface the semiconductor die with a matrix of contactprobes.
 66. A method for conductively bonding circuit assembliescomprising: providing an electronic device including a first conductiveelement; providing a substrate including a second conductive element;applying a water-soluble material impregnated with a conductive fillerof discrete particles to at least one of the first conductive elementand the second conductive element; and dehydrating the water-solublematerial to a degree sufficient to provide an at least partiallysolidified bond between the first conductive element and the secondconductive element.
 67. The method of claim 66, further comprisingforming the conductive filler of the water-soluble material fromdiscrete particles of a metal or metal alloy.
 68. The method of claim ofclaim 66, further comprising selecting the water-soluble material tocomprise a polymer or copolymer-based material.
 69. The method of claim66, wherein providing an electronic device comprises providing asemiconductor die.
 70. The method of claim 69, further comprisingprobing a third conductive element on the substrate to test a functionalaspect of the semiconductor die.
 71. A method for conductively bondingcircuit assemblies comprising: providing an electronic device includinga first conductive element; providing a substrate including a secondconductive element; applying a solder paste having discrete particles ofa metal or metal alloy entrained within a flux carrier to at least oneof the first conductive element and the second conductive element; andheating the solder paste to provide an at least partially solidifiedsolder paste structure comprising the discrete particles of a metal ormetal alloy entrained within the flux carrier, wherein the at leastpartially solidified solder paste structure forms a bond between thefirst conductive element and the second conductive element.
 72. Themethod according to claim 71, wherein heating the solder paste comprisesdriving off volatiles in the flux carrier while maintaining theparticles of a metal or metal alloy in a solid state within a matrix ofremaining material of the flux carrier.
 73. The method of claim 71,wherein providing an electronic device comprises providing asemiconductor die.
 74. The method of claim 71, further comprisingprobing a third conductive element on the substrate to test a functionalaspect of the electronic device.
 75. A method for testing an electronicdevice comprising: providing an electronic device including a firstconductive element; providing a substrate including a second conductiveelement; applying a conductive or conductor-filled liquid, gel or pasteto at least one of the first conductive element and the secondconductive element; bonding the first conductive element to the secondconductive element with the conductive or conductor-filled liquid, gelor paste; passing an electrical signal through the conductive orconductor-filled liquid, gel or paste to test a functional aspect of theelectronic device.
 76. The method of claim 75, further comprisingselecting the conductive or conductor-filled liquid, gel or paste tocomprise a resin, epoxy or RTV adhesive-based material.
 77. The methodof claim 75, wherein providing an electronic device comprises providinga semiconductor die.
 78. The method of claim 77, further comprisingprobing a third conductive element on the substrate to test a functionalaspect of the semiconductor die.
 79. A circuit bonding materialcomprising a water-soluble, polymer or copolymer-based materialimpregnated with a conductive filler of discrete particles.
 80. Thecircuit bonding material of claim 79, wherein the conductive filler ofdiscrete particles comprises discrete particles of a metal or metalalloy.
 81. A circuit assembly comprising: a semiconductor die includingat least one conductive I/O element; a substrate including at least oneconductive attachment pad; and an at least partially solidifiedwater-soluble material bonding a peripheral edge of the semiconductordie to the substrate and holding the at least one conductive I/O elementagainst the at least one conductive attachment pad.